This is a protocol to determine the effect of insulin-induced hypoglycemia on cardiac contractile function and electrical conduction in patients with insulin-dependent diabetes. Specifically, the study will assess the effect of insulin-induced hypoglycemia on left ventricular diastolic and systolic function, and determine the effect of hypoglycemia on the development of abnormal conduction patterns that might promote arrhythmia. The effects of hypoglycemia in the diabetic patients will be compared to those in normal matched volunteers.